Clementine was the first U.S. spacecraft launched to the Moon in over 20 years (since Explorer 49 in June 1973). Also known as the Deep Space Program Science Experiment (DSPSE), the spacecraft was designed and built to demonstrate a set of lightweight technologies, such as small imaging sensors, for future low-cost missions to be flown by the Department of Defense. Clementine carried 15 advanced flight-test components and 10 science instruments.

After launch, the spacecraft remained in Earth orbit until 3 February 1994, at which time a solid-propellant rocket ignited to send the vehicle to the Moon. After two subsequent Earth flybys on 5 February and 15 February, Clementine successfully entered an elliptical polar orbit on 19 February with a period of 5 days and a perilune (closest approach to the Moon) of 400 kilometers. In the following two months, it transmitted about 1.6 million digital images of the lunar surface; in the process, it provided scientists with their first look at the total lunar landscape, including polar regions.

After completing 297 lunar orbits, controllers fired Clementine's thrusters on 3 May to inject it into a rendezvous trajectory in August 1994 with the asteroid 1620 Geographos. Due to a computer problem at 14:39 UT on 7 May that caused a thruster to fire and use up all propellant, the spacecraft was put into an uncontrollable tumble at about 80 rpm with no spin control. Controllers were forced to cancel the asteroid flyby and return the vehicle to the vicinity of Earth. A power supply problem on 20 July further diminished the operating capacity of the vehicle.

Eventually, lunar gravity took control of Clementine and propelled it into heliocentric orbit. The mission was terminated in June 1994 when falling power supply levels no longer allowed clear telemetry exchange.

On 3 December 1996, the Department of Defense announced that Clementine data indicated that there was ice in the bottom of a permanently shadowed crater on the lunar south pole. Scientists estimated the deposit to be approximately 60,000 to 120,000 cubic meters in volume, comparable to a small lake that is 4 football fields in surface area and 5 meters deep. This estimate was very uncertain, however, due to the nature of the data.

Key Dates

19 Feb 1994: Lunar Orbit Insertion

3 May 1994: Departure from Lunar Orbit

Status: Partial Success

Fast Facts

Clementine was the first U.S. lunar mission in more than two decades.

Clementine was the first spacecraft to photograph the Moon's south polar region.

Clementine found evidence suggesting that ice exists in a permanently shadowed crater at the lunar south pole.